1. Field of the Invention
The present invention relates to a complex and an application thereof and, more particularly, to a platinum complex, a manufacturing method thereof, a platinum catalyst, and a platinum catalyst on supports constructed thereby.
2. Description of the Related Art
Platinum has a stable chemical property even in high temperature. Platinum will not react with oxygen, sulfide, strong acids or strong bases in room temperature. In current petrochemistry and energy industry, platinum (Pt) is used as catalysts.
In petrochemistry industry, Pt catalysts are used to increase amount of petroleum. Most of petroleum refineries have catalytic equipment coating with Pt catalysts. When vaporied crude oil flows through catalytic equipment, Pt will catalyze vaporied crude oil to any desired forms. Moreover, most of gas-cleaning facilities for vehicles use ceramic honeycomb coating with Pt and Pd alloy to transfer carbon monoxide (CO) and hydrocarbon into carbon dioxide and water.
In energy industry, shortage of global petroleum is getting serious. Therefore, the development of fuel cells for commercial purpose is attracting more attention. The fuel cells, especially proton exchange membrane fuel cells (PEMFC) are considered as a main source of green energy and only emits harmless carbon dioxide, water and air.
Hydrogen and oxygen are used as fuels of the fuel cells. Pt catalysts are coating on electrodes of the fuel cells so that the fuel cells can generate electrical energy by executing electrochemical reaction with catalytic action of Pt catalysts. In electrochemical reaction, hydrogen in anode side of the membrane electrode assembly (MEA) is decomposed into hydrogen ions and electrons. At the cathode side, oxygen is reacted with the hydrogen ions and the electrons to form water. If total surface area of catalysts can be increased, catalytic performance of Pt catalysts can be improved so that the reacting amount of hydrogen and oxygen per unit area can be increased. Therefore, current density can be increased.
However, in nature, Pt generally exists in a form of a pure state. As a result, surface area of Pt in the form of the pure state can not reach requirement for catalysts. Therefore, further processes are needed to obtain nanoparticles of Pt catalysts. By increasing surface area of Pt, using amount of Pt catalysts can be reduced.
Conventional manufacturing method of Pt catalysts is using chloroplatinic acid as a raw material to produce nanoparticles of Pt catalysts. Usually, chloroplatinic acid can be obtained by dissolving Pt in aqua regia with over amount of hydrochloric acid (HCl) wherein aqua regia is a mixing solution of nitric acid and hydrochloric acid with volume ratio 1:3. Due to chlorine ions in aqua regia can induce the formation of a Pt complex, [PtCl6]2−, Pt can be dissolved in aqua regia. Reaction equation is shown as following: 3 Pt+16 H++4 NO3−+18 Cl− □ 3 [PtCl6]2−+4NO+8 H2O. Next, the Pt complex, [PtCl6]2− is reacted with sodium nitrate (NaNO3) to generate PtO in the temperature 500° C. Following the reduction reaction, PtO is heated to 560° C. for pyrolysis so that PtO can be reduced to form Pt catalysts.
Conventional manufacturing method of Pt catalysts as described above, the oxidation-reduction reaction is taken place between [PtCl6]2− and NaNO3 to produce PtO. However, Pt (II) ions of PtO are very active so that random aggregation between Pt (II) ions happens easily. Therefore, the number of aggregation between Pt (II) ions is hard to control. After completing the reduction reaction, particle sizes of Pt catalysts are still too big and the distribution of particle sizes is too wide so that surface area of Pt and uniformity can not be increased. Moreover, the stability and catalytic activity are low.
In order to solve problems described above, another conventional manufacturing method of Pt catalysts is provided. Pt is absorbed onto supports with the high electrical conductivity such as carbon black to form Pt catalysts on the supports. By dispersing Pt on the supports, stability, catalytic activity, surface area and ability to bear loading can be enhanced.
Currently, using carbon black as the supports has been studied for several years. Catalysts of carbon-black-supported Pt can be abbreviated as Pt/C catalysts, and Pt/C catalysts have well dispersion, fine particles and low manufacturing method etc. Pt/C catalysts are commonly used in proton exchange membrane fuel cell (PEMFC).
Conventional manufacturing method of Pt/C catalysts is dissolving chloroplatinic acid in a deionized water acting as a solvent and then mixing a suitable amount of carbon black into the solvent to get a solution. After the solution is stirred well, the solvent is evaporated. Following, in the reduction reaction, hydrogen is used as reductant to form Pt/C catalysts.
However, in the above conventional manufacturing method of Pt/C catalysts, the reduction reaction is executed right after chloroplatinic acid is mixed with carbon black so that random aggregation between Pt (II) ions still happens easily. Therefore, particle size distribution is still too wide and Pt (II) ions are easy to agglomerate. Furthermore, dispersion of Pt/C catalysts is not even so that surface area of Pt/C catalysts still can not be increased resulting in low catalytic activity.
Taiwan Patent No. 565471 entitled “Processing of high-performance platinum catalyst” illustrates another conventional manufacturing method of Pt/C catalysts. Chloroplatinic acid is dissolved in deionized water and then adding sodium carbonate, and sodium bisulfate into deionized water orderly to form a mixing solution. Following, more sodium carbonate is added into the mixing solution to form a precipitate of Na6Pt(SO3)4. Next, the precipitate of Na6Pt(SO3)4 is dissolved in water and put into an ion exchange resin to replace sodium ions with hydrogen ions and obtain a solution of the precipitate having Pt (II) ion. Following, carbon black, which is graphited in high temperature, is added into the solution of the precipitate and stirred well. Following, hydrogen peroxide (H2O2) acting as a reactant is added in a reduction reaction step. Besides, a drying step is executed by filtering the solution of the precipitate to get the precipitate and then a dried precipitate is obtained by baking. Finally, hydrogen is used in the reduction reaction with temperature being limited between 200 and 250° C. so that Pt/C catalysts with uniform dispersion and small particle size can be obtained.
However, the above conventional manufacturing method of Pt/C catalysts is still directly mixing chloroplatinic acid with carbon black and then processing the reduction reaction to get Pt/C catalysts. Therefore, random aggregation between Pt (II) ions still happens easily resulting in the wide distribution of particle sizes and poor dispersion etc. Therefore, overall surface area of Pt/C catalysts is still too small and catalytic activity thereof is low. Moreover, this conventional method is focused on interaction between carbon black and Pt, which used to consider as keypoint to affect dispersion, growth and structure of Pt particles. In fact, controlling Pt particles within a narrow distribution should be the most important factor to affect catalytic activity of Pt/C catalysts, current density and power of the fuel cells.